Preparation of acetophenone from alpha-methyl styrene



Patented Feb. 27, 1951 PREPARATION OF ACETOPHENONE FROM ALPHA-METHYLSTYRENE George R. Bond, Jr., Paulsboro, N. J assignor to Houdry ProcessCorporation, Wilmington, Del.,

7 a corporation of Delaware Application January 31, 1947,

No Drawing.

Serial No. 725,726

2 Claims.

The present invention is primarily concerned with the preparation ofcertain nitrogenous addition compounds of aralkenes as well as with theutilization of these addition" compounds as intermediates for thepreparation of aromatic carbonyl compounds. The invention alsocontemplates starting with crude hydrocarbon mixtures, such as petroleumoil fractions, as source materials for the required nitrogenousintermediates.

I have discovered that olefinic compounds generally, reactquantitatively with nitrogen tetroxide, while only selected types ofolefins, such as aralkene-l compounds, for example styrene and itshomologues, also react quantitatively with nitrogen trioxide as well aswith nitrogen tetroxide. If the reaction is carried out in the presenceof a mixed hydrocarbon fraction, the nitrogenous addition productsthereby formed in either case from these aromatic olefinic compounds canbe readily separated for example from cycloaliphatic and acyclichydrocarbons or their addition products that may be present in thereaction mixture, as well as from unreacted aromatic carbocycliccompounds free from side chain unsaturates. Accordingly, an excellentmethod is thereby provided for preparing hydrocarbon fractions free fromundesired olefinic unsaturates. The nitrogenous addition compoundsformed, furthermore, can be employed as useful intermediates for thepreparation of valuable organic compounds, particularly by conversion tocarbonyl compounds such as aldehydes and ketones, as hereinafterappears. Thus, starting with relatively inexpensive crude hydrocarbonfractions, such as petroleum or other mineral oil distillates, one canreadily obtain not only relatively pure fractions of desired saturatedaliphatic or aromatic hydrocarbons, but in addition a convenient sourceis furnished for important intermediates, and conversion products ofthese intermediates.

The purification of petroleum and other mineral fractions generally, ismore fully described and claimed in my copending application, Serial No.725,725, filed of even date herewith. The present application is moreparticularly concerned with the nitrogenous addition compounds ofaromatic olefins, such as those formed from compounds of the styrenetype.

In accordance with the invention, a hydrocarbon oil containing anaralkene-l compound, such as styrene or its homologues, is treated withan oxy compound of nitrogen selected from the group consisting ofnitrogen trioxide and nitrogen tetroxide under conditions avoidingthermal decomposition. As a result of the principal reaction, theolefinic side chain reacts to form nitroso addition compounds such asnitrosites and nitrosates respectively, which can be easily separatedfrom the unreacted components by steam distillation or other means suchas selective solvent extraction, as will hereinafter appear. Thenitrosites and nitrosates thus formed, with or without previousseparation from the unreacted components, may be further converted inaccordance with the invention to aromatic carbonyl compounds, such asketones and aldehydes, by reaction with an alkaline material, also underconditions avoiding thermal decomposition.

The reaction of the designated nitrogen oxides with the olefinichydrocarbons takes place in either vapor or liquid phase. In suchreactions between aralkene-l compounds and N20: or N204, the addition ofthe nitrogen oxide takes place selectively at the olefinic double bond.According to related reactions described in the literature, with N203the nitroso compounds formed are believed to correspond to the struc- NON02 Nitrosite while with N204 the compounds obtained are believed tohave the structure rat-t- NO 6NO2 Nitrosate Since other tautomericarrangements are also possible and likewise consistent with the observedreactions of these nitroso compounds herein described, the exactarrangements shown in the formulae are not material to the presentinvention, and applicant does not desire to be bound thereby. R in theabove formulae represents a hydrocarbon radical of the benzene series(which may be nonfunctionally substituted) including thereby polycyclichydrocarbon radicals such as naphthalene and alkylated naphthalenes, andthe indicated free bonds may be attached to hydrogen or to alkylradicals.

The physical state of these nitroso compounds depends to a large extentupon their purity. For instance, styrene nitrosites and amethyl styrenenitrosites, when relatively pure, are crystalline; the nitrosates aremore often oily, although in some instances crystalline nitrosates ofstyrene 1% derivatives are obtained. In reactions involving thetreatment of a hydrocarbon mixture containing aralkene-l compounds withN204, the hydrocarbon mixture is contacted with the N204 under suchconditions that the strongly exothermic reaction takes place preferablyin the range of 80 to 100 F. The desired temperature range may beobtained by controlling the rate of admission of the N204 vapors and bythe further provision of heat exchange if necessary or desired. The N20;may be obtained in vapor form from any suitable source such as byvolatilization of liquid nitrogen tetroxide at suitable temperatures.The N204 vapor is introduced directly into the body of the hydrocarbonliquid and thorough contact of the reactants may be enhanced by agitation during treatment. The completion of the reaction is readilyascertained by the cessation of the exothermic phenomenon (significanttemperature decline) and by the marked formation .of brown fumes abovethe surface of the liquid being treated. When it is observed from theseindications that the reaction has gone to completion, further additionof N204 should be stopped. Any excess N204 in the reaction products maybe destroyed by the addition of water to convert the same to nitric andnitrous acids,

'or by other Well known methods such as the addition of aqueoussolutions of sulfamic acid as is done in the azo dye industry, or .bythe addition of aqueous solution of urea to destroy nitrous acid.

The reaction with N20; is conducted generally in a similar manner. N203may be derived from any suitable source, such as by reaction of an acidwith a nitrite under conditions insuring the absence of any oxidizingagent. The nitrogen trioxide is contacted with the olefin-containinghydrocarbon liquid with control of flow rate and temperature similarlyto that described above in the N204 treatment. Completion of thereaction is indicated by the cessation of the exothermic phenomenon orthe appearance of excess N203.

In the case of the nitrosites particularly, separation of the reactionproducts is readily eflected by physical means, since the reactionproducts are generally solids (crystalline), or in cases where gummy oroily materials are formed, they are suinciently different in density andother properties from the unreacted portions to permit physicalseparation. Unless all of the desired nitrogenous addition compoundsformed are solid materials, it is preferred to effect separation bysteam distillation, and even in instances where solid products areinvolved, steam distillation may be employed to advantage.

The described reaction of N203 and N204 takes place not only witharalkene-l compounds but only to a limited extent in some instances, asin the case of cyclo-hexene and di-isobutylene.

I have observed that some of the indicated nitrogenous additioncompounds of olefins, for instance styrene nitrosite, on long standingapparently undergo a rearrangement, since they become less reactive withalkaline substances to form the carbonyl compounds. To obtain maximumyields of the desired carbonyl compounds, therefore, it is preferred toemploy freshly preill 4 pared nitrosites or nitrosates. The character ofthe change which takes place on standing cannot be fully explained, butI have also observed that styrene nitrosite treated with ferrous sulfateor with hydrochloric acid, similarly is rendered lessreactive withalkali to form the carbonyl compounds. Also after refluxing styrenenitrosite in water at or near boiling, only very small yields ofbenzaldehyde are obtained by subsequent reaction with alkaline solutionsand appreciable amounts of nitrobenzene are formed.

The nitrogenous addition compounds formed with either the N203 or N204,are converted to carbonyl compounds such as aldehydes and ketones, inaccordance with the invention, by reaction with an aqueous solution ofan alkaline material. Whether aldehydes or ketones will be formeddepends upon the arrangement of the carbon atoms in the starting olefin,as illustrated by the following equations:

It will be readily understood that it is not necessary to employ a crudepetroleum hydrocarbon raw materials may be used. One of the morimportant advantages of the present invention, however, lies in theability to resort to crude distillates containin the desired olefinspreferably in a fraction of narrow boiling range. Thus, a crude naphthaproduced by high temperature cracking may be solvent extracted toproduce an extract containing aromatic materials including styrene,olefins, and diolefins. By treatment with N204, nitrosates are formed ofthe unsaturated materials, which may then be separated fromsubstantially pure saturated aromatics, inasmuch as the reactions toform these nitroso compounds apparently go to completion. Alternatively,one may employ N203 for the treatment of the solvent extract, wherebythe nitrosites of the styrene type compounds and of the conjugateddiolefins are formed, leaving substantially unreacted the mono-olefincontent of the naphtha. The aromatics may be further purified by theremoval of these remaining olefins by treatment with N204 to form thenitrosates of the olefins. The nitrosates and nitrosites may be removedfrom the treated naphtha as by distillation. Thus, the naphtha may besteam distilled, leaving the nitrosite or nitrosate as a residue. Ifdesired, the nitrosite or nitrosate may be precipitated by dilution ofthe treated naphtha with petroleum ether or the like and then removed asby filtration or decantation. Alternatively, the nitrosate or nitrositein the treated naphtha may be decomposed and the unreacted portions ofthe naphtha then separated, as by distillation.

Although nitroso compounds of the type above described are decomposedthermally to an uncontrollable variety of diiferent decompositionproducts, in accordance with the present invention, an entirelydifferent type of decomposition is effected by reaction of the nitrosocompounds with aqueous alkaline materials, under controlled conditions.Temperatures at which the nitroso compounds tend to undergo thermaldecomposition should be avoided to favor good yields of the desiredcarbonyl derivatives. Any of a number of inorganic bases or alkalinematerials may be employed for effecting the decomposition of the nitrosocompound, such as alkaliand alkali earth metal hydroxides or carbonatesand alkali metal bicarbonates; for example, caustic soda, sodiumcarbonate, sodium bicarbonate; calcium carbonate, magnesium carbonate,etc. Although ammonium hydroxide is operative for the purpose, loweryields are generally obtained therewith because of side reactions of NH3with the nitrosates or nitrosites.

Organic bases would be expected to have the same tendency to sidereactions as occurs with the ammonium hydroxide. For maximum yields, topreclude or diminish side reactions, it is preferred to employ the morestrongly alkaline materials in dilute aqueous solution.

For optimum results, the quantity of alkaline material employed shouldbe about or at least that furnishing hydroxyl ions in an amount which isthe molal equivalent of the nitroso compound to be reacted. A lesseramount of alkaline material, being insufiicient to react with all of thenitrogenous product present, naturally results in reduced yields. Toogreat an excess of alkaline material on the other hand alsoprogressively decreases the yield because of the increasing tendency topromote side reactions. It was found as a general rule that good yieldswere obtainable with aqueous solutions of sodium hydroxide in an amountabout double the weight of the nitrosate or nitrosite present.

In the initial reaction of the N203 or N204 with the olefin containingfraction, a wide range of temperatures may be employed; formation ofnitroso compounds have been obtained at temperatures ranging from below32 F. (with liquid butene) to somewhat above 130 F. It is preferred,however, to carry out the reaction at about room temperature or slightlyabove as in the range of 80 to 100 F. At low temperatures the yields arepoorer and less stable reaction products are obtained, while attemperatures above 100 F. the tendency towards undesirable sidereactions increases. The use of superatmospheric pressure is unnecessaryand it is preferred to carry out the reaction at atmospheric pressure orif desired at subatmospheric pressures. Higher pressure may be used whenit is not extended to the point of causing undesirable side reactionssuch as oxidation, nitration, and others which may occur. The reactionof the nitrogen oxides with the indicated unsaturated hydrocarbonsproceeds rapidly so that time limitations are imposed only by operatingconditions to assure completeness of the reaction. For complete reactionthe amount of nitrogen oxide, whether it be N: or N204, should be atleast one mol of the oxide for each bond of olefinic unsaturation.Excess nitrogen oxide should be destroyed, as described.

No universal rule can be stated as to the choice between the use of N203and N204 in the formation of the nitroso compound as an intermediate. Itwas found that better yields of benzaldehyde Were obtainable fromstyrene nitrosite, whereas in the preparation of acetophenone betteryields were obtained from a-methyl styrene nitrosate than from thecorresponding nitrosite. The reaction of the styreneand a-methyl styrenenitroso compounds with aqueous alkaline solutions to yield respectivelybenzaldehyde and acetophenone begins to take place at room temperature;at higher temperatures the reaction proceeds more rapidly. In the caseof benzaldehyde and similar products which are recovered by steamdistillation, the reaction is preferably conducted simultaneously withsuch distillation. Temperatures above those encountered in steamdistillation should in any event be avoided; although formation of thealdehyde does occur at the higher temperature, the yield of purealdehyde is decreased because of undesirable side reactions such aspolymerization of the aldehyde, formation of sodium benzoate, or thelike. In the case of acetophenone and like compounds, conditions similarto those described in connection with benzaldehyde are preferablyemployed. Even if the separation of the aldehyde or ketone is not to beeffected by steam distillation, it is nevertheless advisable to avoidthe higher temperatures in the reaction of the nitroso compound with thealkaline material. The reaction of the alkaline material with nitrosateor nitrosite occurs relatively independently of pressure, so thatpressure considerations are concerned mainly with the equipmentlimitations, time of operation, and temperature limitations.

The selectivity and efiectiveness of the described nitrosation'method inremoving olefinic unsaturates from hydrocarbon mixtures, is illustratedby the following typical experiment:

Example I A sample of a synthetic mixture of paraffinnaphthene base(acid treated gasoline range material) containing 10% styrene, wastreated with N203 until excess of nitrous fumes showed completion ofreaction. The precipitate formed during the reaction was separated byfiltration and the residual oil, 90% by volume of the original, waswashed with about 5 volumes of 10% caustic solution, then washed with asmall amount of sodium bisulphite solution to remove traces ofbenzaldehyde, again washed with a small amount of 10% caustic solution,then water washed to remove excess caustic, dried over calcium chloride,and distilled to 294 F. cut-point. The distillate had the followingproperties, indicating complete removal of styrene.

Refractive index (11. 1.4189 Specific gravity (di 0.7523 Bromine number(ASTM), 0.0

Specific dispersion, Y- 99 In the above example the reference to acidtreated gasoline range material denotes a residue resulting fromtreatment of a gasoline fraction with acid in conventional manner foranalytic determination of the amount of aromatics and olefins by theirabsorption in the treating acid. The residue consisted essentially ofparaffins and naphthenes, which residue was washed and neutralized, thendried. This washed residue gave no reaction with nitrogen oxides and wastherefore satisfactory as a diluent or carrier for olefinic materialsbeing tested.

To further show the selectivity of the reaction of the designatednitrogen oxides with olefinic materials preliminary experiments werecarried out with aromatic hydrocarbons, such as benzene, which werefound to be substantiall non-reactive.

The formation of the nitroso compounds with olefinic unsaturates presentin a crude hydrocarbon distillate, and the production of carbonylcompounds therefrom. are illustrated in the following examples:

Example II A hydrocarbon synthetic mixture which included approximately10% styrene and 90% acid treated gasoline range material was treatedwith N203 at room temperature until presence of excess N203 indicatedcompletion of reaction. The crystalline precipitate which formed, wasseparated by filtration, Washed with water, petroleum ether, andalcohol, and dried in vacuum at room temperature. A part of the nowwhite to cream colored crystalline precipitate was mixed with aqueousNaOH solution (approximately 20 cc. NaOH solution per gram ofprecipitate) and the resulting mixture was distilled until no more oilcame over with the water. The distillate contained a colorless oilslightly heavier than water and with a strong odor of benzaldehyde.

To identify the benzaldehyde, the distillate was made slightly basicwith a small amount of NaOH aqueous solution and then oxidized with coldsaturated KMnOr solution which was added in small increments until thepersistence of the purple permanganate color indicated substantiallycomplete oxidation of the solution.

The oxidized solution was acidified with H01 (conc.) and decolorizedwith I-I2SO3. A white crystalline precipitate formed upon acidificationExample III A hydrocarbon fraction, distilled from a sample ofdehydrogenated cumene boiling entirely at 260 F. at atmospheric pressureand containing approximately 90.0% a-methyl styrene was treatwith N204with cooling to prevent temperature rise above 100 F. until excess N204fumes indicated completion of reaction. The weight of the sampleincreased to 156% during this treatment. The treated sample was washedwith water to remove excess N; and unreacted hydrocarbons separated bysteam distillation; the residue being the nitrosate. This liquidresidue, specific gravity 1.23, was treated with approximately twice itsvolume of 10% NaOH solution and steam distilled. The distillate, whichwas identified as impure acetophenone, contained 80% by volume ofmaterial boiling within the range of 393 to 397 R, which portionamounted to approximately by volume of the original a-methyl tyrene.

This product is sufiiciently pure for most industrial uses ofacetophenone. Further purification may be effected, if desired, in theusual manner, for instance by redistillation or solvent extraction, or acombination of these steps.

Erample- IV A sample of a-methyl styrene nitrosi-te wasobtained byreacting a hydrocarbon fraction, similar to that used as the startingmaterial in the preceding example, with N203 at room temperature untilcompletion of the reaction between the N203 and the hydrocarbon wasevidenced by no further evolution of heat on absorption of the N203.This methylstyrene nitrosite wa purified in similar manner to the,preceding example and the ketone formed by reaction with sodiumhydroxide solution as before. The only odor of the product was that ofacetophenone, but the purity was considerably less than that obtainedfrom the corresponding nitrosate as indicated by the boiling range inwhich 80% Was found to boil between 354 F. and 405 F.

A purer nitroso compound can be obtained by a treatment of the originalolefin-containing fraction with S02 prior to the treatment with thenitrogen oxide, the S02 treatment being carried out generally asdescribed in my U. S. Patent 2,410,042 of October 29, 1946. Thefollowing example further illustrates the combined treatment.

Example V (A) A synthetic sample comprised of by volume of reformernaphthafrom the destructive distillation of coal and 10% by volume ofadded styrene was subjected to treatment at room temperature with N203,to segregate the styrene as the nitrosite. When completion of thereaction was indicated by presence of excessN20a, the precipitate formedwas recovered by filtration. The results of two such treatments on:portions of this sample showed removal of styrene (as the nitrosite) inamounts of, respectively, 9.7 and 10.1%. Discrepancies in yieldsindicate presence of impurities, in the gummy precipitate, which wereremoved by washing the precipitate prior to drying.

(B) Another portion of the original sample was saturated with S02 gas atapproximately room temperature. After standing for about two andone-half hours, the oil was decanted from the small amount of blackishprecipitate which had formed and settled during standing. The oil waswashed several times with water and then washed twice with 10% by volumeportions of 10% NaOH solution to remove excess S02. The separated oilwas then subjected to a steam distillation. The recovered oil amountedto about 91% of the original sample.

The treated and distilled oil was then subjected to treatment with N202in the same manner as the treatments effected on the samples in theparagraph (A). This time a fine white precipitate of styrene nitrositewas obtained. An alcohol extraction of the crystalline precipitateshowed the presence of only traces of impurities. The result of thisfinal treatment showed the removal of styrene (as the nitrosite), asbased on the original sample, of 10.9 indicating the presence of a smallamount of styrene in the reformer naphtha. The experiment furtherindicated that purer styrene nitrosite is obtained by the preliminarytreatment of theoil with S02.

The original sample had a bromine number of 34.4. After treatment inparagraph (A) the residual oil had bromine number of 18.1, while aftertreatment in section (B) it had a bromine number of 16.1.

The above described combined treatment with S02 and nitrogen oxide canbe advantageously employed where the nitroso compound or carbonylderivative therefrom is desired in unusually pure form. In addition, itwill be understood that with a purer form of the nitroso compound betteryields of the desired carbonyl compound requiring less extensivepurification, are obtained.

Obviously many modifications and variations of the present invention ashereinbefore set forth may be made without departing from the spirit andscope thereof and therefore only such limita- 9 tions should be imposedas are indicated in the appended claims.

The present application is a continuation-inpart of my application,Serial No. 528,948 filed March 31, 1944, now abandoned.

I claim as my invention:

1. The method of producing acetophenone which comprises reacting ahydrocarbon fraction rich in a-methyl styrene with N204 to form anitrosate of said a-methyl styrene, continuing the reaction undercontrolled conditions maintaining the temperature thereof not in excessof 100 F. and until excess N204 forms indicating completion of thereaction, steam distilling the product to separate unreactedhydrocarbons leaving a residue containing said nitrosate, treating saidresidue with about twice its volume of 10% NaOH solution and steamdistilling the alkaline reaction mass, thereby obtaining a distillatecontaining acetophenone.

2. The method in accordance with claim 1 wherein said hydrocarbonfraction is a purified GEORGE R. BOND, JR.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,313,719 Beckham Mar. 16, 19432,322,308 Moyer June 22, 1943 2,402,315 Crowder June 18, 1946 OTHERREFERENCES Wieland Berichte, vol. 36, Part 2, pages 2558 2567 (1903).

1. THE METHOD OF PRODUCING ACETOPHENONE WHICH COMPRISES REACTING AHYDROCARBON FRACTION RICH IN A-METHYL STYRENE WITH N2O4 TO FORM ANITROSATE OF SAID A-METHYL STYRENE, CONTINUING THE REACTION UNDERCONTROLLED CONDITIONS MAINTAINING THE TEMPERATURE THEREOF NOT IN EXCESSOF 100* F. AND UNTIL EXCESS N2O4 FORMS INDICATING COMPLETION OF THEREACTION, STREAM DISTILLING THE PRODUCT TO SEPARATE UNREACTEDHYDROCARBONS LEAVING A RESIDUE CONTAINING SAID NITROSATE, TREATING SAIDRESIDUE WITH ABOUT TWICE ITS VOLUME OF 10% NAOH SOLUTION AND STEAMDISTILLING THE ALKALINE REACTION MASS, THEREBY OBTAINING A DISTILLATECONTAINING ACETOPHENONE.